Control systems for battery operated vehicles

ABSTRACT

In some control systems for controlling the supply of electrical energy from a battery to the electric motor of a vehicle it is desirable in certain circumstances to use the maximum available current which may be in excess of that available through a thyristor type D.C. switch. Rather than increase the rating of the D.C. switch to cope with these occasional demands there are provided a by-pass contactor having contacts which, when closed, shunt the D.C. switch, means operable by a speed controller in its maximum speed demand condition included in an enabling circuit of the by-pass contactor and time delay means for delaying the energisation of the by-pass contactor as a function of the motor current.

United States Patent 1191 Morton et al. Oct. 9, 1973 [54] CONTROLSYSTEMS FOR BATTERY 3,500,161 3/1970 Domann et al. 318/341 X OPERATEDVEHICLES 3,349,309 10/1967 Dannettell 3,297,930 1/1967 Payne 318/341 x[75] Inventors: John Morton, Hazel Grove; Keith Drummond Stevens,Marple; Graham Spencer Thexton, Marple f Mlner Bridge, a" of EnglandAssistant Examiner-H. Huberfeld AttorneyH0lman & Stern [73] Assignee:Cableform Limited, Romiley, Stockport, Cheshire, England [57] ABSTRACT[22] Filed: Jan. 20, 1972 l f n h I f In some contro systems or contromg t e supp y o [21] Appl' 219513 electrical energy from a battery tothe electric motor of a vehicle it is desirable in certain circumstancesto [30] Foreign Application Priority Data use the maximum availablecurrent which may be in Jan. 20, 1971 Great Britain 2,812/71 excess thatavailable thmugh a thyristor type switch. Rather than increase therating of the DC. 521 11.5. c1 313/139, 318/341, 318/391, Switch withthese caskmal demands here 318/395, 318/400 are provided a by-passcontactor having contacts 51 1111. C1. H02p 7/28, H02p 1/04 which whencksedi Shunt the Swlich, means 53 Field of Search 318/139, 341, 332,arable by a Speed in its maximum Speed mand COl'lditiOIl included in anenabling circuit Of thC by-pass contactor and time delay means fordelaying [56] References cued the energisation of the by-pass contactoras a function UNITED STATES PATENTS the mom current 3,517,290 6/1970Gunsser 318/341 X 8 Claims, 1 Drawing Figure AM P CONTROL SYSTEMS FORBATTERY OPERATED VEHICLES This invention relates to the control systemsfor controlling the supply of electrical energy from a battery to themotor of vehicle.

it is known to control the supply of current to the motor utilizing aD.C. switch including thyristors which supply pulses of current underthe control of pulse generator, the frequency and/or mark-space of thepulses generated being varied in accordance with the desired currentflow to the motor.

In some operational condition the maximum current provided by such aD.C. switch is not sufficient and it is desirable to connect the motordirectly across the battery by means of a by-pass contactor the contactsof which shunt the D.C. switch.

An object of the present invention isto provide an improved controlsystem which enables the use of a bypass contactor operable in certainconditions.

According to the invention, a control system for the electric motor of abattery operated vehicle, comprises a D.C. switch for controlling thesupply of current from a battery to the electric motor, a by-passcontactor having contacts which, when closed, shunt the D.C. switch,means operable by a speed controller in its maximum speed demandcondition included in an enabling circuit of the by-pass contactor andtime delay means for delaying the energisation of the by-pass contactoras a function of the motor current.

Conveniently, the time delay is proportional to the motor current.

An embodiment of the invention will now be described with reference tothe accompanying drawing which is a schematic circuit diagram of acontrol system for a fork-lift truck.

The armature A of an electric drive motor is connected in series, viathe contacts ctl of a forward- /reverse contactor CTl, with thefieldwinding F, a D.C. switch S and a small resistor R10, across a battery B.The forward/reverse contactor CTl is energised via a start microswitchMSl on the speed control pedal of the vehicle, trip relay contacts rlbl,other interlock relay contacts represented by contacts rlcl and aforward/reverse switch F/R S.

Shunting the D.C. switch and the resistor R10 are the contacts ct2 of aby-pass contactor CT2 and it is required that the contactor should beenergised only in the following conditions.

1. start microswitch M8,, trip relay contacts rlbl, other interlockcontacts rlcl are closed and forward or reverse is select on switch F/RS.

2. speed control pedal is completely depressed so closing a by-passmicroswitch M82.

3. a sufficient time has elapsed from starting to supply current to themotor to prevent the motor being started via the by-pass contactor.

With conditions 1 and 2 met the base bias on a transistor T is removedvia diodes D5 and D6 or D7 so that transistor T is switched off and acapacitor C1 is free to charge.

As disclosed in our copending application Ser. No. 74456 filed Sept. 22,1970, now abandoned, and in continuing application No. 272,882 of July18, 1972, a voltage proportional to mean motor current is taken fromseries resistor R10 and compared with a reference voltage VRrepresenting a threshold current l After the threshold is exceeded, andamplifier AMP with feedback H provides an output signal which iscombined in unit E with the demand signal VD from the speed controlpedal to provide a modified control signal to the D.C. switch S. Unit Eis prior art and constitutes any known comparator circuit providing adifference signal output as used in typical servo systems. The amplifieroutput is also connected to one end of a potentiometer supplying thebase of a transistor T5 so that the collector current is reduced as theamplifier output increases. The collector load is a resistor R and thecapacitor Cl which is now free to charge in a time inverselyproportional to the motor current and therefore torque. It is requiredthat the time for the by-pass contactor to close in large for high motorcurrent or torque and reduces with fall in current.

Transistors T2 and T3 together with diode D1 and resistor R2 form abi-stable switching circuit which is initially in the condition of bothtransistors being switched off. When the voltage on capacitor C1 reachesa predetermined level, transistors T2 and T3 become conductive so thatrelay RLA is energised, the rlareal thereof completing the circuit ofby-pass contactor CT2. Due to the inhibiting action of diode D3 on clamptransistor T relay RLA remains energised and by-pass contactor CT2 canbe opened and closed solely by means of microswitch MS2 at the extrememovement of the speed controller until such times as the switches andcontacts F/R S, rlcl, rib] and MSI are opened. This releases relay RLAby enabling clamp transistor T1 to become conductive and dischargecapacitor Cl.

Transistor T4 is used to switch off D.C. switch S prior to operation ofby-pass contactor CT2 and to ensure that it remains off until by-passcontactor CT2 can be opened.

The arrangement in accordance with the invention may with advantage beused with the arrangement of our co-pending application Ser. No. 74457now abandoned, and its continuation Ser. No. 272,882 which shows a D.C.switch with D.C. gating of the cummutating thyristor. In such acombination the commutating capactior (shown as C1 in the figures of thedrawing of application Ser. No. 74457 and application Ser. No. 272,882as a suppression capacitor and considerably reduces the arcing of theby-pass contactor contacts.

What is claimed is:

l. A control system for the electric motor of a battery operatedvehicle, comprising a D.C. switch for controlling the supply of currentfrom a battery to the electric motor, a by-pass contactor havingcontacts which, when closed, shunt the D.C. switch, means operable by aspeed controller in its maximum speed demand condition included in anenabling circuit of the by-pass contactor and time delay means fordelaying the energisation of the by-pass contactor as a function of themotor current.

2. A system as claimed in claim 1, wherein a signal proportional to themotor current controls the delay time of the time delay means, a clampmeans being provided to prevent the time delay means from operatinguntil predetermined conditions are met.

3. A system as claimed in claim 1, wherein a signal proportional to themotor current controls the rate of charge of a capacitor which remainsclamped by clamping means until predetermined control contacts areclosed and the speed controller is in its maximum demand condition.

4. A system as claimed in claim 3, wherein the signal proportional tothe motor current is obtained by including a resistor in the currentpath of the motor, the voltage developed across the resistor being usedto control the current through a transistor included in the chargingpath of the capacitor.

5. A system as claimed in claim 3, wherein the clamping means comprisesa transistor connected across the capacitor and being conductive untilsaid predetermined conditions are met.

6. A system as claimed in claim 3, wherein the voltage developed acrossthe capacitor due to charging is fed to a bi-stable switching circuitwhich changes state when the capacitor voltage reaches a predeterminedlevel and thereby causes energisation of a relay having contactsincluded in the energisation circuit of the bypass contactor.

7. A system as claimed in claim 4, wherein the voltage developed acrossthe resistor in the path of the motor current is compared with areference voltage representing a threshold current the resultant signal,when the voltage representing the motor current exceeds the referencevoltage, being used to control the charging of the capacitor.

8. A system as claimed in claim 1, wherein means is provided toswitch-off the DC. switch immediately prior to operation of the by-passcontactor and to ensure that it remains off until the by-pass contactorcan be opened.

1. A control system for the electric motor of a battery operatedvehicle, comprising a D.C. switch for controlling the supply of currentfrom a battery to the electric motor, a by-pass contactor havingcontacts which, when closed, shunt the D.C. switch, means operable by aspeed controller in its maximum speed demand condition included in anenabling circuit of the by-pass contactor and time delay means fordelaying the energisation of the by-pass contactor as a function of themotor current.
 2. A system as claimed in claim 1, wherein a signalproportional to the motor current controls the delay time of the timedelay means, a clamp means being provided to prevent the time delaymeans from operating until predetermined conditions are met.
 3. A sYstemas claimed in claim 1, wherein a signal proportional to the motorcurrent controls the rate of charge of a capacitor which remains clampedby clamping means until predetermined control contacts are closed andthe speed controller is in its maximum demand condition.
 4. A system asclaimed in claim 3, wherein the signal proportional to the motor currentis obtained by including a resistor in the current path of the motor,the voltage developed across the resistor being used to control thecurrent through a transistor included in the charging path of thecapacitor.
 5. A system as claimed in claim 3, wherein the clamping meanscomprises a transistor connected across the capacitor and beingconductive until said predetermined conditions are met.
 6. A system asclaimed in claim 3, wherein the voltage developed across the capacitordue to charging is fed to a bi-stable switching circuit which changesstate when the capacitor voltage reaches a predetermined level andthereby causes energisation of a relay having contacts included in theenergisation circuit of the by-pass contactor.
 7. A system as claimed inclaim 4, wherein the voltage developed across the resistor in the pathof the motor current is compared with a reference voltage representing athreshold current the resultant signal, when the voltage representingthe motor current exceeds the reference voltage, being used to controlthe charging of the capacitor.
 8. A system as claimed in claim 1,wherein means is provided to switch-off the D.C. switch immediatelyprior to operation of the by-pass contactor and to ensure that itremains off until the by-pass contactor can be opened.